This invention pertains to heat recovery steam generators, and pertains particularly to modular type steam generators utilizing multiple pairs of parallel offset headers having tubes attached to alternate sides of each pair of upper and lower headers.
Heat recovery steam generators (HRSG) are used to provide efficient utilization of the heat content from exhaust gases of stationary gas turbines, such as used for electrical power generation. By extracting heat from the turbine hot exhaust gas, the HRSG produces steam which is used for various purposes such as for driving steam turbines to produce more electricity or space heating. In such installations, large gas turbines provide a very favorable return on investment. However, large gas turbines require large heat recovery steam generators, which generally exceed maximum dimensional limits for overland shipping of shop manufactured units. Usual alternatives to field construction for such a heat recovery steam generator are not economical, as an important factor in the favorable economics of such gas turbine installations is that the total time from power plant concept to operation should be short and result in a desirable quick return on investment.
Heat recovery steam generators which could be easily assembled from large, shippable size modules would be economically desirable. However, when such units are attempted, many design complications occur requiring field welding of high boiler pressure headers and tubing, or the addition of costly baffles and structural parts which cause resistance to the exhaust gas flow, thereby adding to the uncertainty of operation, reducing reliability, reducing power production from the gas turbine and adding to costs for heat recovery steam generator (HRSG) installation.
Various arrangements of tubular type heat exchangers for steam generators have been previously developed and used. For example, U.S. Pat. No. 2,336,833 to Badenhausen discloses a conventional waste heat steam generator having multiple vertical parallel tubes each connected to horizontal upper and lower headers. U.S. Pat. No. 2,926,493 to Poole et al discloses a similar steam generator enclosed within a casing for utilizing waste heat from a gas turbine exhaust. Also, U.S. Pat. No. 4,054,107 to Horlitz, Jr. discloses a compact waste heat steam generator system using serpentine shaped tubes arranged for marine type installations. However, the prior art has apparently not provided a waste heat recovery steam generator which utilizes pairs of horizontal parallel offset headers having vertical tubes to provide shippable modules of factory assembled units for efficient, low cost field installation.